The present invention relates to a cutting tool for machining by chip removal consisting of a substrate of cemented carbide, cermet, ceramics, cubic boron nitride based material, or high speed steel, and a hard and wear resistant refractory coating of which at least one layer comprises a hexagonal MeX-phase formed in-situ during the deposition either as a single phase or by co-deposition together with a second phase. This finding can be used in several ways giving a high degree of possibilities to tailoring the properties of the finished tool, for example, as hexagonal structure particles in a coating matrix of another type, or of the same type, of crystal structure, or as separate layers within a multilayer superstructure. Since the hexagonal type of structure has different mechanical and chemical properties than for instance a cubic structure, the combination of different types of crystallites can give completely new properties compared to a single structure material.
The majority of all PVD-layers used today for metal cutting for machining by chip removal consists of crystalline TiN, Ti(C,N), and (Ti,Al)N with a cubic NaCl type structure. However, a metastable (Ti,Al)N layer will at elevated temperature, during heat treatment or at service if sufficient amount of energy is supplied, phase separate into c-TiN and h-AIN. These precipitates of a h-AIN and/or c-AIN can act as hardeners in the layers. It has been demonstrated that an optimised amount of precipitates of c-AIN and/or h-AIN in a cubic c-(Ti,Al)N matrix will improve the performance of the layer as disclosed by EP-A-1400609 and EP-A-1452621. However, the volume occupied per atom in the hexagonal (wurtzite type) structure is 25% larger than in the cubic structure (NaCl type). Therefore, if the degree of structural transformation of an applied (Ti,Al)N layer proceeds too far this may lead to cohesive failure and accelerated wear of the layer.
It is an object of the present invention to provide a coating comprising at least one layer containing a h-MeX phase to be applied to a cutting tool for machining by chip removal.
It is a further object of the present invention to provide a method for depositing layers comprising an h-MeX phase using PVD technology.
It has been found that, by balancing the chemical composition, the amount of thermal energy and the degree of ion induced surface activation during growth, growth rate, and pressure, layers containing h-MeX phase can be obtained which, compared to the prior art, display enhanced performance in metal cutting. The layers comprise crystals of h-MeX with or without the co-existence of c-NaCl type structures of nitrides and/or carbides and/or oxides. The layers are deposited using PVD-technique, preferably by arc evaporation.